1. Field of the Invention
The present invention relates to a method for testing drilling compounds, particularly drilling fluids and cements, to determine the drilling compounds ability to seal the porous formations around the borhole.
2. General Background
In the art of drilling oil and gas wells, the borehole of the well is drilled into and through various types of formations, ranging from the granite rock type to very soft and porous earth before making contact with the actual pocket of oil and gas being sought. The industry has developed drilling compounds, in particular drilling fluids and cements which are pumped down into the well hole, as the drilling is ongoing, one of the functions which is to seal the formation around the hole in order to keep the hole free of matter and to have a clean borehole during the drilling process.
The ability of a particular drilling fluid or cement to seal a formation is determined by the percent and size of solids present in the drilling fluid and cement. This is crucial since if a particular drilling fluid is being utilized in an attempt to seal a formation that is very porous, and the particular drilling fluid in question does not contain the necessary percent in size of solids, then the fluid will be unable to seal the formation, and in some cases the entire whole drilling fluid and cement will be lost to the formation until the solids present in the drilling fluid and cement form a seal in the porous formation. This loss of drilling fluid and cement can be a major expense item in the drilling of an oil well, and therefore, it is absolutely crucial that the proper drilling fluid be utilized in order to ensure that when it is put down in the hole that it is not lost and that it seals the formation.
Therefore, prior to the introduction of great amounts of expensive drilling fluid into the borehole, it is crucial that the fluid undergoes a test to ensure that the percent in size of solids in the drilling fluid will be suitable for that particular formation and seal it. At present, there are no tests available which would allow one to determine the size particles and number of particles per a certain volume of drilling fluid. The present methods incorporate the using of a specially hardened filter paper disk to filter drilling fluid. This paper is so constructed that it will filter out colloidal and sub-micron size particles. Therefore, no accurate reading can be made using this particular method.
The following are summaries of U.S. Patents which may be considered to be pertinent art in the field:
U.S. Pat. No. 3,503,933 issued to Whitten, entitled "Formation-Sampling Apparatus", teaches the use of a fluid sampling apparatus to obtain samples of the well bore surface with the apparatus obtaining the sample by being dropped down hole and boring into the borehole wall.
U.S. Pat. No. 3,565,169 issued to Bell, entitled "Formation-Sampling Apparatus", also teaches the use of an improved apparatus for obtaining samples of the wall of a borehole by being dropped down hole and boring into the wall for obtaining the requisite sample to be tested.
U.S. Pat. No. 3,352,361 issued to Urbanosky, entitled "Formation Fluid-Sampling Apparatus", discloses an apparatus having a tubular probe member for movement into sealing engagement with earth formation to obtain samples of formation fluids if any therein. It functions quite like the previous apparatuses.
U.S. Pat. No. 3,011,554 issued to Desbrandes et at, entitled "Apparatus for Investigating Earth Formations", also is a tube dropped down hole for sampling earth formation fluids. A portion of the formation that is being sampled is seal from the drilling fluid until the rest of the sample is obtained.
U.S. Pat. No. 2,829,518 issued to Ruble et al, entitled "Subsurfaces Flow Meter", is also a down hole tube for sampling formation wall and determining fluid flowing from a subsurface formation. It actually measures the rate of a flow of fluids passing through the well bore.
U.S. Pat. No. 3,677,080 issued to Hallmark, entitled "Sidewall Well-Formation Fluid Sampler", relates to an improved formation fluid sampler of the type that is lowered into a well on wire line and directed to sidewall well formation fluid sampler with the ability for obtaining contamination free samples as compared with other samples in the art.
U.S. Pat. No. 3,653,436 issued to Anderson et al, entitled "Formation Sampling Apparatus", is an improved apparatus like that disclosed in the U.S. Pat. No. '933 and U.S. Pat. No. '169 patent for sampling well formations down hole.
U.S. Pat. No. 3,254,531 issued to Briggs, entitled "Formation Fluid Sampling Method", relates to a method a sampling content of earth formations by lowering an apparatus down hole and piercing the earth formation for obtaining requisite sample.